Walls in between may or may not be necessary... and they don't have to be full height either, maybe just a half wall "extension" would be enough to provide some privacy.
Suggestion for how to angle the top piece, use hinges to attach it to the window sill above, and then if you have all the side walls lower but at the same height (I have my sides cut to match the angle but it's not necessary for this), it'll naturally rest on top of them at an angle. This is assuming the piece of wood on top can be removed without too much work...
Suggestion for how to angle the top piece, use hinges to attach it to the window sill above, and then if you have all the side walls lower but at the same height (I have my sides cut to match the angle but it's not necessary for this), it'll naturally rest on top of them at an angle. This is assuming the piece of wood on top can be removed without too much work...